It has been found that when testosterone and endorphins in ejaculated semen meet the cervical wall after sexual intercourse, females receive a spike in testosterone, endorphin, and oxytocin levels, and males after orgasm during copulation experience an increase in endorphins and a marked increase in oxytocin levels. This adds to the hospitable physiological environment in the female internal reproductive tract for conceiving, and later for nurturing the conceptus in the pre-embryonic stages, and stimulates feelings of love, desire, and paternal care in the male (this is the only time male oxytocin levels rival a female's).[1]

Positive correlations between positive orgasm experience in women and testosterone levels where relaxation was a key perception of the experience. There is no correlation between testosterone and men’s perceptions of their orgasm experience, and also no correlation between higher testosterone levels and greater sexual assertiveness in either sex.[3]

An increase in T levels has also been found to occur in both men and women who have orgasms that are masturbation-induced.[4][5]

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Studies conducted on rats have indicated that their degree of sexual arousal is sensitive to reductions in testosterone. When testosterone-deprived rats were given medium levels of testosterone, their sexual behaviors (copulation, partner preference, etc.) resumed, but not when given low amounts of the same hormone. Therefore, these mammals may provide a model for studying clinical populations among humans suffering from sexual arousal deficits such as hypoactive sexual desire disorder.[6]

In one study, almost every mammalian species examined demonstrated a marked increase in a male's testosterone level upon encountering a novel female. P.J. James et al. investigated the role of genotype on such so-called reflexive testosterone increases in male mice. They also concluded that this response is related to the male's initial level of sexual arousal.[7]

In non-human primates it has been suggested that testosterone in puberty stimulates sexual motivation, which allows the primate to increasingly seek out sexual experiences with females and thus creates a sexual preference for females.[8] Some research has also indicated that if testosterone is eliminated in an adult male human or other adult male primate's system, its sexual motivation decreases, but there is no corresponding decrease in ability to engage in sexual activity (mounting, ejaculating, etc.).[8]

Higher levels of testosterone were associated with periods of sexual activity within subjects, but between subjects testosterone levels were higher for less sexually active individuals.[9] Men who have sexual encounters with unfamiliar or multiple partners experience large increases of testosterone the morning after.[10]

Men who watch a sexually explicit movie have an average increase of 35% in testosterone, peaking at 60-90 min after the end of the film, but no increase is seen in men who watch sexually neutral films.[11] Men who watch sexually explicit films also report increased optimism and decreased exhaustion.[12] Based on previous research that has found a link between relaxation following sexual arousal and testosterone levels,[13]

Testosterone increases in men who engage in brief conversations with women. This result was seen in heterosexual men who had engaged in sexual activity in the 6 months prior to the study. The increase in T levels was associated with the amount of “courtship” behaviours that the men exhibited.[14]

Men’s levels of testosterone, a hormone known to affect men’s mating behaviour, changes depending on whether they are exposed to an ovulating or nonovulating woman’s body odour. Men who are exposed to scents of ovulating women maintained a stable testosterone level that was higher than the testosterone level of men exposed to nonovulation cues. Testosterone levels and sexual arousal in men are heavily aware of hormone cycles in females.[15] This may be linked to the ovulatory shift hypothesis,[16] where males are adapted to respond to the ovulation cycles of females by sensing when they are most fertile and whereby females look for preferred male mates when they are the most fertile; both actions may be driven by hormones.

When males are exposed to either visual or auditory erotic stimuli and asked them to complete a cognitive task, where the number of errors on the task indicated how distracted the participant was by the stimuli. They concluded that men with lower thresholds for sexual arousal have a greater likelihood to attend to sexual information and that testosterone may have an impact by enhancing their attention to the relevant stimuli.[17]

Sperm competition theory: Testosterone levels are shown to increase as a response to previously neutral stimuli when conditioned to become sexual in male rats.[18] This reaction engages penile reflexes (such as erection and ejaculation) that aid in sperm competition when more than one male is present in mating encounters, allowing for more production of successful sperm and a higher chance of reproduction.

Androgens may modulate the physiology of vaginal tissue and contribute to female genital sexual arousal.[19]

Women’s levels of testosterone are higher when measured pre-intercourse vs pre-cuddling, as well as post-intercourse vs post-cuddling.[20]

López, Hay, and Conklin (2009) found that women who are non-pill users experience a significant increase in testosterone levels in response to viewing a video of an attractive man courting a young woman. This was in comparison with the control conditions.[3]

When females have a higher baseline level of testosterone, they had higher increases in sexual arousal levels but smaller increases in testosterone, indicating a ceiling effect on testosterone levels in females. Sexual thoughts also change the level of testosterone but not level of cortisol in the female body, and that hormonal contraceptives may have an impact on the variation in testosterone response to sexual thoughts.[21]

Van Anders and Dunn (2009) also studied the link between testosterone and orgasms in women, and found a correlation between high T levels and positive orgasm experience. This occurred in both the partnered and solitary context of orgasm.[3]

There is a time lag effect when testosterone is administered, on genital arousal in women. In addition, a continuous increase in vaginal sexual arousal may result in higher genital sensations and sexual appetitive behaviors.[22]

Testosterone may prove to be an effective treatment in female sexual arousal disorders.[23] There is no current androgen preparation or for the treatment of androgen insufficiency approved by the FDA at this point in time, but it has been used off-label to treat low libido and sexual dysfunction in older women. Testosterone may be a treatment for postmenopausal women as long as they are effectively estrogenized.[23]